The treatment of chemical waste is a topic of vital concern to industry and to all those concerned with the environment. Increasingly, governmental regulations are aimed at controlling the type and quantity of waste materials generated by industry because of the potential effect on the environment. As a result, treatment methods which reduce or eliminate chemical waste are of great interest to industry.
The paint and coatings industry is a major source of chemical wastes. Paint sludges are produced in the automotive industry, appliance industry, metal fabricating industry and during the painting of wood products, outdoor structures such as bridges and lamp posts, and all types of industrial equipment. For example, it is estimated that nearly 40% of the 6 gallons of paint used to produce the exterior finish on an automobile ends up as waste. With an estimated 36 million cars built each year (not including light trucks and other vehicles), the waste generated from automobile painting alone approaches one quarter of a billion pounds. If this waste paint could be turned into a useful product, a major source of chemical waste could be reduced or eliminated.
When an automobile is painted on an assembly line, the excess paint is collected beneath the automobile in a trough filled with water. Typically, the waste paint solids are recovered by placing the paint-water mixture into large settling tanks. The paint solids either agglomerate as a raft on the surface of the water, or they sink and accumulate on the bottom of the tank. Other methods for treating the paint-water mixture to remove the paint solids are disclosed in U.S. Pat. Nos. 3,764,013 and 4,100,066. The material recovered from such processes is known as paint sludge.
Paint sludge is very complex material. The paint component contains uncured polymer resins, pigments, curing agents, surfactants, and other minor formulation ingredients. In addition, paint sludge contains water and a variety of organic solvents. The presence of the uncured paint resins, which cure and form a film upon heating, make the sludge very sticky and difficult to handle. Therefore, detackification agents are often added to the sludge.
The detackified paint sludge is usually disposed of without further processing. It is a tackfree, pulpy, putty-like solid having about 25-75% volatiles (water and organic solvent) content. The cost and the environmental impact of disposing of paint sludge in this form make it undesirable.
Recently, a process was developed in which the detackified sludge is converted to a dry powder prior to disposal. The first step of this process, which is disclosed in U.S. Pat. No. 4,980,030, involves removing a portion of the water and liquid hydrocarbons from the sludge. The high solids sludge is then heated to remove the remaining water and hydrocarbons. The heating step is also designed to cure the uncured polymeric paint resins. The process is advantageous because it reduces the volume of waste produced, and the resulting powder is somewhat easier to handle than the wet sludge.
A similar process is disclosed in U.S. Pat. No. 5,087,375, which discloses a method for producing insoluble raw materials from waste. Among the materials which may be so treated is paint sludge. Specifically disclosed is a method of treating, handling, heating and calcining paint sludge. Further, at column 8, lines 52-56 of U.S. Pat. No. 5,087,375, it is indicated that product from the process may be used as a filler for sealants.
However, both U.S. Pat. No. 4,980,030 and U.S. Pat. No. 5,087,375, completely cure any uncured polymers in the paint sludge during their heating and/or calcining steps. Accordingly, the resulting product is an inert, inorganic, hard, abrasive particulate material.
An improvement on the processes disclosed in U.S. Pat. Nos. 4,980,030 and 5,087,375 is found in copending application Ser. No. 763,324. There the product produced, which may be used as a filler in sealant compositions, contains uncured polymer. As explained in that application, keeping the polymer uncured results in a product which is soft and easily dispersible. Further, the uncured polymer in the product renders the resultant filler "functional" with regard to chemical reactivity and binder content. This permits use of the resultant product in sealant formations without the need to add expensive "functional ingredients" which would otherwise have to be added along with the inert fillers.
Still, the process of copending application Ser. No. 763,324 requires certain treatment and processing steps in order to produce a putty or powder filler which is then added to the sealant composition. It would be desirable to minimize or eliminate the need for such steps and have available an in.situ method for using a paint sludge as a functional filler in preparing sealant compositions.
Accordingly, the need remains for a simplified method for making a sealant from paint sludge and for a sealant composition made by that method.